True triaxial tests on transversely isotropic unsaturated loess

In order to study the mechanical properties of transversely isotropic unsaturated remolded loess under complex stress paths, two groups of 15 tests are carried out using the true triaxial apparatus. The first group consists of 9 tests, each of which includes two stages: the sample is pre-consolidated by K₀ under the constant vertical pressure, and then the true triaxial consolidated drained shear tests with the constant suction, net confining pressure and intermediate principal stress parameter are carried out. The second group of 6 tests are the true triaxial shear ones with the constant water content under different shear rates and the constant suction, net confining pressure and intermedium principal stress parameter. The test results show that all the stress-strain curves in the true triaxial consolidated drained shear tests are hardening type and in hyperbolic form, and the hardening trend is more obvious with the increase of the intermedium principal stress parameter. All the samples are in shear contraction state during the shearing process, and the water content of the samples decreases with the shearing process. The water content-axial strain relationship curve of the samples before failure can be approximated as a straight line. In the true triaxial shear tests with the constant water content, the loading rate has few effects on the basic form of the stress-strain curve, but has certain effects on the stiffness of the samples, which are not monotonous, so there may be a critical rate. In the shear process, the volume of the samples decreases continuously, and the saturation increases with the increase of the deviatoric stress, so the pore water pressure increases and the suction decreases continuously. The research results may provide useful reference for the establishment of constitutive model and strength criterion for the transversely isotropic unsaturated loess and its engineering application.